Where to find correct syntax for operator in Blender API manual?
The docs have this information if you know what you're looking for. 

http://www.blender.org/api/blender_python_api_current/.../wm.call_menu

In this case TextEditor > Templates > Python > UI Menu has a working example of how to trigger a specific menu 

The UI source is often the most comprehensive documentation. For example space_view3d.py's class VIEW3D_MT_mirror(Menu) shows how to pass properties to an operator. As you have now seen

props = layout.operator("transform.mirror", text="Z Global")
props.constraint_axis = (False, False, True)
props.constraint_orientation = 'GLOBAL'


Here both constraint_axis and constraint_orientation are passed as values to bpy.ops.transform.mirror as soon as the button is pressed.